Two 50 Gal Parallel HWTs w/ Softener + Thermostatic Mix Valve

[KillSwitch]

Welcome open and honest feedback from experts on my attached diagram to parallel two 50 gal electric tanks with thermostatic mixer, using 10 micron house filter and water softener.

I prefer the two 50 gal tank vs an 80 or 100. Both tanks will be set at 140 deg.

Welcome questions and feedback. Hope to improve on this setup the best I can before install.

 

[Reach4]

You are not allowed to tee the T&P valve drains.

You show your own 3-valve bypass for the softener. If you do that, you don't need to buy a bypass for the softener.

You are allowed to run unmixed hot water to a dishwasher or washing machine, but not any sinks where people stick their hands.

 

[Sponsor]

 

[Jeff H Young]

Haven't done parallel in a while but been told to keep every thing equidistant on cold feed and hot output. not sure how critical it is but been suggested to keep everything equal. and keep T and P separate. ball valve between filter and softener probably could do without , a good 1 inch valve probably cost you 15 bucks or more . if thermal expansion tank is required it must be downstream of your shutoff valve , So I'm guessing that may mean 2 expansion tanks.

 

[Jadnashua]

In reality, you should get more hot water if you run the tanks in serial versus parallel. The reason is, the last tank will be filling with hot water, so you'll get the full volume out of it plus at least 70-80% of the second one, equaling nearly 90% of the total volume in your tanks. When they are in parallel, with the incoming cold water feeding each, you can only get about that 70-80%, but now, that's your maximum total.

It's really tough to keep everything balanced when you have them in parallel, which means you'll be dropping your output sooner with the aggregate sum. It's also simpler. You may want to add the complexity to isolate one or the other tank. The first tank may wear out sooner, as it would need to run longer and more often than the outlet tank, so bypassing it may be an advantage to continue to have hot water while that one is replaced.

 

[KillSwitch]

Revisions:
- Separated the T&P valves
- Will search for the washer and dishwasher lines and connect to hot if feasible
- Added 2x two gallon expansion tanks downstream of shutoffs valves

Series vs Parallel is an interesting topic. My understanding, Series is preferred when adding a 2nd tank (different size) to existing to accommodate demand. Parallel is recommended for 2 same size tanks and yes both supply and delivery lines must ALL be the same length.

Attached 2 pager I found online from Rheem: Parallel vs Serial setup instructions.

Posting V2 diagram which includes your recommended changes. Welcome added feedback. Thanks!